In the fabrication of aircraft and other structures using carbon fiber composite materials, it may be necessary to apply paint, other coatings, or adhesives to the surface of the composite material. However, during the application of paint, other coatings, or adhesives to the surface of a composite material the presence of moisture may compromise the strength of the adhesion between the coating and the material. Therefore, it may be necessary to characterize the moisture levels of composite material surfaces prior to application of coatings or adhesives to the surfaces.
Conventional methods of measuring moisture on surfaces of composite materials include cutting and weighing samples of the material to infer water content on like-sized parts or coupons of the material. Other methods may include heating the samples and measuring the quantity of moisture which is evaporated from the samples. Infrared and microwave electromagnetic radiation can be used to interact with moisture. The terahertz regime at higher frequency offers particular sensitivity.
Many non-conducting, dry materials that are opaque to infrared and visible light exhibit low absorption in the terahertz (THz) frequency range. The terahertz frequency range is commonly described as 1×1011 to 1×1013 Hz (1 to 0.01 mm wavelength). Absorption of radiation in the THz frequency range increases with the quantity of moisture on the surface of a material.
Accordingly, a moisture detection system and method are needed which utilize absorption of radiation in the THz frequency range by moisture to facilitate stand-off, non-contact and non-destructive characterization of moisture levels on composite materials.
The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings